The present invention relates to automated pneumatic tire production systems and, more particularly, to methods and apparatus for automated production of tread-belt assemblies.
The tread making process for pneumatic tires typically involves separately building a package out of green (uncured) rubber including a belt package of one or more tread belts or xe2x80x9cbreakersxe2x80x9d plus a tread applied over the belts to form a belt-tread package. Because the belts are intended to be essentially inextensible, the belt-tread package is formed separately on a second stage tire building machine, and then applied to a green tire carcass already assembled on a first stage tire building machine. Then the tire carcass is xe2x80x9cblown upxe2x80x9d into a toroid shape within the belt-tread package and sent to a mold where the entire assembly is cured into the final tire. Examples of this process are disclosed in U.S. Pat. Nos. 5,141,587, 5,3544,404, 5,554,242, and 6,139,668.
When the belt-tread package is built, the tread is supplied as xe2x80x9ctread stockxe2x80x9d material which is a continuous strip of green rubber. The continuous strip must be cut to the right length, preferably at an angle, for splicing cut end to cut end to form a closed circle covering the belt package. Typically, the belt package is on a cylindrical assembly drum, and a leading end of the tread stock must be moved over to be positioned properly for wrapping around the outer circumference of the belt package on the assembly drum. An example is set forth in EPO 0, 387,455. Difficulties to be overcome in this operation include holding the tread stock which is soft and tacky, and maneuvering the tread stock from a supply reel or conveyor into proper position on the belt package. This maneuvering typically involves lifting the leading end of the tread stock which is time consuming and can deform the tread undesirably.
The tread stock is generally cut to length with a cutting blade of some sort. Modern equipment has improved the cutting process by using ultrasonic vibration of the cutting blade, but this introduces a new problem. The ultrasonic vibration of the blade causes significant heating in any material touching the ultrasonically driven blade. In particular, where the cut surfaces of the tread stock touch the sides of the cutting blade, ultrasonic heating induces partial curing of the green rubber. This is undesirable because the cut surfaces must be spliced together to form a complete, circular tread, and partially cured spliced surfaces of otherwise green rubber may not fuse together properly during a subsequent tire curing process. It is known to partially address this problem by blowing air in between the cutting blade and the adjacent cut surface. For a blade cutting at an angle, this will work on top of the blade by lifting the cut end of tread stock up away from the blade, but under the blade there is no where for the tread stock to go and it cannot be separated from the blade unless it is deformed or compressed.
It is an object of the present invention to improve the tread making process by addressing the above-described problems in the cutting and moving of the tread stock for application to, and splicing together on, the outer circumference of a belt package.
According to the invention, a method for making a tread-belt assembly for a pneumatic tire comprises the steps of: using a supply ramp to supply green rubber tread stock for application on a substantially cylindrical green rubber belt package; advancing the green rubber tread stock along the supply ramp toward the substantially cylindrical green rubber belt package; positioning at least a final portion of the supply ramp substantially along a plane tangent to an outer circumference of the substantially cylindrical green rubber belt package; and applying the green rubber tread stock to the outer circumference of the substantially cylindrical green rubber belt package by moving a leading cut end of the green rubber tread stock from the supply ramp to the substantially cylindrical green rubber belt package along the plane tangent to the outer circumference of the substantially cylindrical green rubber belt package.
According to the invention, the method further comprises the steps of: holding the green rubber tread stock from above for moving the leading cut end of the green rubber tread stock, and inserting a plurality of transfer pins downward into both lateral outer edges of the green rubber tread stock such that each transfer pin is angled toward a closest laterally outside edge of the green rubber tread stock for holding the green rubber tread stock. Each transfer pin is angled at an angle in the range of 20 degrees to 80 degrees, preferably in the range of 40 degrees to 60 degrees, and most preferably at an angle of 45 degrees.
According to the invention, a method for making a tread-belt assembly for a pneumatic tire comprises the steps of: using a supply ramp to supply green rubber tread stock for application on a substantially cylindrical green rubber belt package; advancing the green rubber tread stock along the supply ramp toward the substantially cylindrical green rubber belt package; securing the green rubber tread stock for cutting; and cutting the green rubber tread stock using an ultrasonically driven cutting blade such that a wedge of space is created between a back side of the cutting blade and the cut surface of an adjacent cut end of the green rubber tread stock.
According to the invention, the method further comprises the steps of: creating the wedge of space by moving a cutting edge of the cutting blade along a first plane which coincides with the cut surface of the adjacent cut end of the green rubber tread stock; and orienting the back side of the cutting blade such that the back side coincides with a second plane which is angled forward from the first plane by an acute cutting blade angle xcex1 the cutting blade angle xcex1 is within the range of 1 degree to 15 degrees, and preferably within the range of 3 degrees to 8 degrees.
According to the invention, the method further comprises the steps of: blowing air to create a wedge of space between a front surface of the cutting blade and the cut surface of an adjacent cut end of the green rubber tread stock; and securing the green rubber tread stock by inserting a plurality of holding pins into the green rubber tread stock. Preferably, the plurality of holding pins is inserted from below the green rubber tread stock; the cutting blade cuts downward from above the green rubber tread stock; and a roller attached to the cutting blade prevents the green rubber tread stock from lifting when the plurality of holding pins is inserted from below. Optionally, the roller is also used to guard the cutting blade.
According to the invention, the method further comprises the steps of: positioning at least a final portion of the supply ramp substantially along a plane tangent to an outer circumference of the substantially cylindrical green rubber belt package; and applying the green rubber tread stock to the outer circumference of the substantially cylindrical green rubber belt package by moving a leading cut end of the green rubber tread stock from the supply ramp to the substantially cylindrical green rubber belt package along the plane tangent to the outer circumference of the substantially cylindrical green rubber belt package.
According to the invention, apparatus for making a tread-belt assembly for a pneumatic tire comprises: a supply ramp means for supplying green rubber tread stock for application on a substantially cylindrical green rubber belt package; means for advancing the green rubber tread stock along the supply ramp means toward the substantially cylindrical green rubber belt package; means for securing the green rubber tread stock for cutting; and an ultrasonically driven cutting blade for cutting the green rubber tread stock such that a wedge of space is created between a back side of the cutting blade and the cut surface of an adjacent cut end of the green rubber tread stock.
According to the invention, the apparatus further comprises means for creating the wedge of space by moving a cutting edge of the cutting blade along a first plane which coincides with the cut surface of the adjacent cut end of the green rubber tread stock; and by orienting the back side of the cutting blade such that the back side coincides with a second plane which is angled forward from the first plane by an acute cutting blade angle xcex1.
According to the invention, the apparatus further comprises: a plurality of holding pins for securing the green rubber tread stock by inserting the plurality of holding pins into the green rubber tread stock. The apparatus further comprises: means for inserting the plurality of holding pins from below the green rubber tread stock; means for moving the cutting blade downward from above to cut the green rubber tread stock; and means attached to the cutting blade which guard the cutting edge, and which also prevent the green rubber tread stock from lifting when the plurality of holding pins is inserted from below.
According to the invention, the apparatus further comprises: means for positioning at least a final portion of the supply ramp means substantially along a plane tangent to an outer circumference of the substantially cylindrical green rubber belt package; and means for applying the green rubber tread stock to the outer circumference of the substantially cylindrical green rubber belt package by moving a leading cut end of the green rubber tread stock from the supply ramp means to the substantially cylindrical green rubber belt package along the plane tangent to the outer circumference of the substantially cylindrical green rubber belt package.
Other objects, features and advantages of the invention will become apparent in light of the following description thereof.